Digital pre-distortion (DPD) is a technology to increase efficiency in RF power amplifiers and suppress frequency re-growth generated by power amplifier non-linear effects. This technology has been widely used in modern cellular network base station for GSM, CDMA, WCDMA and LTE standards. In order to increase the power amplifier efficiency the requirements for the memory taps and non-linear polynomial order for Volterra kernels based digital pre-distortion become more and more complicated. The digital computations increase exponentially with the number of Volterra Kernels. The adaption converge time has been significantly increased. The 3G cellular networks require very fast DPD converge time to handle the dynamic changes of modulation schemes, PA output power levels and multi-carrier configurations. The Volterra kernels are usually predetermined in the lab or in the manufacturing calibration stage, and usually there is a very large number to support all the modulation standards like CDMA, GSM, WCDMA and LTe, all of the multicarrier configurations and all power amplifier output power levels and power amplifier aging versus time changes. These predetermined Volterra kernels are usually not orthogonal and have significant correlations between each other.
DPD usually uses various adapt algorithms to calculate the coefficients of Volterra kernels. Volterra kernels are expressed in terms of some kinds of orthogonal polynomials in order to have a faster converging speed and better performance. Orthogonal polynomials add redundancy due to the higher order forms containing lower order forms. These factors significantly limit DPD performance.